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TRANSCRIPT
VETIVER SYSTEM PROTECTS ESTUARY DIKES IN THE MEKONG DELTA, VIETNAM
Paul Truong TVNI Technical Director Pham Thanh Hai
Chief Engineer, Dike Department, Bac Lieu Province, Vietnam
June 2015
INTRODUCTION
The estuarine region of the Mekong River in the Mekong Delta is a low lying and flat area, which is subjected to daily Ldal movement. Thus rendering it an ideal locaLon for aquaculture, parLcularly prawn (shrimp) farming.
Due to its flat topography, dikes are needed to protect the prawn ponds from daily Ldal movement, king Ldes, Ldal surge during the rainy season and occasional typhoons.
These dikes are built mostly from locally dredged alluvial materials, silt and silty clay, which are highly erodible. So they are oSen breached and required regular and costly maintenance and rebuilding.
When properly implemented and maintained, the following presentaLon clearly shows the effecLveness of the VeLver System in stabilising and protecLng two dikes: one for 12 years and another for 8 years from the adverse elements menLoned above.
A typical estuarine flat at the mouth of the Mekong River in the Mekong Delta, with naLve vegetaLon:
Mangrove on low area and salt tolerant species on higher
ground
Established prawn ponds
New prawn ponds
This photo was taken in June 2007, four years aSer the construcLon of this 11km long dike. It was built as a trial site to determine the suitability of VS in stabilising its ba]ers
VeLver grew well on the sea facing (outside)
ba]er, which was subjected to king Ldes and occasional Ldal
surges
VeLver grew well on the inside ba]er, which was not
subjected to king Ldes and Ldal surges
This outside ba]er was subjected to regular king Ldes and occasional Ldal surges with highly saline brackish water (not full strength sea water).
VeLver survived and thrived under this condiLon.
Water level during king Lde
Eight Years Later
The same dike 12 years aSer the construcLon (8 years aSer the previous
photos) showing excellent veLver growth
According to the dike maintenance engineer,
veLver planLng stabilised the ba]ers, as well as keeping the dike surface drier and firmer thus more stable during
the wet season
Excellent veLver growth on both inside and outside ba]ers
Excellent veLver growth in dry season and up to 2m tall in the
wet season
Inside ba]er
Outside ba]er
NEW DIKE June 2007
Following the success of the trial, the local authority embarked on building a much larger and longer dike: 42km long, to protect a
series of new ponds
ConstrucLon of new dike started in June 2007
Eight Years ASer PlanLng
A very well protected dike and stable road
Outside ba]er
Inside ba]er
MAINTENANCE
It is obvious that prawn farmers benefit greatly from VeLver
planLng, it also provided an economic incenLve to other farmers living along the dike. By law, farmers are not allowed to dig up or destroy veLver plants but they are free to harvest it for their own uses such as fodder, mulch, thatch or string making and burning to control weeds, as well as grazing their stock on the ba]ers.
VeLver harvested for fodder in the dry season
Regrowth aSer harvesLng even in the
dry season
Burning to control weeds in the dry season
Regrowth aSer burning to control weeds
Heavily grazed in the dry season
PLANTING DESIGN
The recommended planLng design for ba]ers like these is one row near the edge of the road and one at its foot. The space in between to be planted in rows on contour, with VI between 0.8-‐1.0m, depending on slope gradient.
Although these photos show that either the planLng was not carried out as recommended or veLver died out, it has successfully stabilised these ba]ers, indicaLng that veLver root mass is more important than contour rows in stabilising relaLvely low gradient and short slope, such as these ba]ers.
Growth in the wet season
Keeping road free from debris
CONCLUSION AND RECOMMENDATION
When properly implemented and maintained, VeLver System is very effecLve in stabilising and protecLng estuarine dikes from the adverse elements commonly experienced in coastal zone.
ParLcipaLon of local populaLon is the key element to its success. This involves educaLon, providing guidelines, instrucLons and support to the local people.
Last but not least, the enforcement of a firm regulatory program by the local authority